Superconducting Quantum Computer Beckons

PORTLAND, Ore. — The first demonstration of high-temperature superconductivity in the surface of a topological insulator -- a promising material for quantum computers -- was reported this week by Lawrence Berkeley National Laboratory (Berkeley Lab).

Topological insulators are a unique class of new materials whose bulk properties are that of an insulator, but whose top layer is conducting. Their advantage for future quantum computers is that they are predicted to support what are called Majorana zero modes, which would make the q-bits stored there nonvolatile.

Quantum computers hold the promise of easily solving the kind of combinatorial problems that are difficult for conventional computers -- such as sifting through vast databases -- which today requires that computers check and compare each record separately. However, quantum computers could sift through all records simultaneously, picking out the optimal solution is a single step.

Unfortunately, the q-bits used in quantum computers are very fragile, and subject to a phenomenon called decoherence, which destroys their reliability at quickly finding optimal solutions; fixing the unreliability requires sophisticated error-correction techniques.

Now, Berkeley Lab used its Advanced Light Source (ALS) has confirmed that a bismuth selenide topological thin film heterostructure, made at China's Tsinghua University (Beijing) in the laboratory of Xi Chen and Qi-Kun Xue using molecular beam epitaxy, is a high-temperature superconductor that may house Majorana zero modes opening the door to its potential use for future quantum computers.

"Up until now, these Majorana zero modes have just been theoretical," said Alexei Fedorov, a staff scientist for ALS at Berkeley Lab in an interview with EE Times. "We have characterized this new material and found that it is a good candidate to look for Majoran zero modes. The next step will be to set up an experiment to look for this effect."

Majoran zero modes, which are naturally immune from decoherence, would enable fault-tolerant quantum computers to be more easily built, since the q-bits stored there would be non-volatile.

Other researchers on the project include Eryin Wang of Tsinghua University, who is currently an ALS doctoral fellow in residence at Berkeley Lab, as well as other Tsinghua University researchers, including Shuyun Zhou Hao Ding and Xi Chen. Funding was provided by the National Natural Science Foundation of China.

The Advanced Light Source (ALS) at Berkeley Lab is a unique resource that has many demanding experiments lined up to use it. The researchers there set up contraptions like the one illustrated to perform one experiment, then reconfigure the equipment for the next experiment. They have probably completely reworked the whole set-up by now :)

It kind of reminds me of my bedroom back when I was in high school. I was a very messy kid...

We still seem to be working the very low levels of quantum computers. Is the architectural structure that would use these low levels worked out? I can't imagine that this would be a Von Neumann architecture, so what would this beast we are calling a quantum computer look like? How would programmers write code to use it?

Most of the architecture work today is based on the assumption that massive error correciton algorithms will have to be implemented to deal with the unpredictability of quantum decoherence. However, if Majorana zero modes are found in this superconducting topological insulator, then decoherence will no longer a problem and more conventional architectures could prevail. We'll have to wait and see if Majorana zero modes are found and can be appropriatley harnessed.

Maybe I'm way off, but would these computers be subject to effects due to random alpha particle strikes? Would seem to me that error correction would be necessary in any case where alpha particles or other random high energy particles could interfeer with otherwise 'perfect' theoretical models. Anyone know?

Your may be right, but no one is sure how stable these Majorana zero modes will be. However, without them they will need error correction between each stage of a circuit, since quantum decoherence happens even without interference.

Well D-Wave has the advantage of being here now, but is a specialized solution only useful for certain tasks, whereas if the topological insulators are found to have usable Majorana zero modes, then they would represent a comprehensive solution on which a quantum computer industry could be built. Of course, D-Wave is following all these promising research paths, so might even be first to make use of them.